1. Field of the Invention
The present invention relates to syringes which are capable of operating selectively in either a freely reciprocating mode or a restricted, threaded mode. More particularly, the present invention relates to a locking syringe that incorporates on the plunger thereof a triggering device which may be actuated to retract threads on the plunger, thereby to enable the plunger to move with respect to the barrel in a freely reciprocating rather than in the restricted, threaded mode. The invention has ready application to the field of angioplasty.
2. The Background of the Invention
One of the most basic of the tools used by the medical practitioner is the syringe. Perhaps best known as an instrument used with a needle to inject medicine into a patient, the syringe has also been found useful in a variety of other applications. For example, syringes are particularly useful in performing angiographic procedures.
Angioplasty is a procedure for reducing the blockage which may occur in blood vessels. Over time, blood vessels may become partially or totally blocked due to buildup of cholesterol plaque along the walls of the vessel.
One location where plaque buildup is particularly dangerous is within the coronary arteries. The coronary arteries are those arteries which supply oxygen-rich blood to the heart. Buildup of plaque within the coronary arteries, a condition commonly referred to as coronary artery disease, can cause serious chest pain--angina--and, if not treated, may eventually cause heart failure.
Coronary angioplasty involves opening these blocked coronary arteries by inserting a balloon-tipped catheter into the artery. The balloon is inserted by making an incision usually in the groin or arm. A catheter is then inserted in a blood vessel exposed by the incision and threaded into the coronary artery.
An x-ray sensitive dye is injected into the coronary artery to enable the clinician to accurately position the catheter in the blocked portion of the artery. The catheter is inserted along the artery until the section of the catheter on which the balloon is located is positioned along the blocked portion of the artery.
A fluid is injected into the catheter to inflate the balloon. As the balloon is inflated, the plaque is compressed thereby expanding the narrowed artery. The clinician then withdraws the fluid from the balloon catheter, causing the balloon to deflate. The balloon catheter may then be removed from the patient.
It has been found that a syringe provides an effective tool for the introduction of fluid into the balloon catheter. As the pressure within the balloon must be carefully controlled during the angioplasty procedure, typical syringes having a plunger which may be freely depressed into the barrel are inadequate for this application.
If the pressure within the balloon is too great, the balloon may burst, a circumstance which usually requires immediate emergency surgery to correct. Some prior art attempts at designing a syringe which provides greater control over the pressures achieved in the balloon include providing a syringe which incorporates a plunger which is threadably connected to the barrel. Thus, the plunger may be slowly threaded into the barrel, resulting in a more controlled introduction of fluid into the balloon catheter.
A serious disadvantage to such syringes is the inability to freely and rapidly move the plunger in and out of the barrel in sliding reciprocation. For example, a preferred method of deflating the balloon is to rapidly withdraw the plunger from the barrel to create a negative pressure, thereby causing the fluid to exit the balloon in an attempt to equilibrate the pressure within the balloon catheter. Withdrawing the plunger gradually from the barrel of the syringe by "unscrewing" the plunger requires a great amount of time and, more significantly, results in reduced effectiveness in deflating the balloon.
In recognition of the desirability of a syringe capable of operating in both a freely reciprocating mode and a restricted, threaded mode, syringes have been developed which employ a threaded engagement mechanism on the barrel of the syringe which can be actuated to selectively engage with and disengage from threads on the plunger.
When the thread engagement mechanism is engaged, the syringe is in its restricted threaded mode, so that free reciprocating movement of the plunger sliding within the barrel is prevented. In this restricted mode of operation, the plunger may only be moved within the barrel by its rotation, which gradually moves it into or out of the barrel.
In many syringes employing a thread engagement mechanism on the barrel, the syringe is awkward to use. When using the syringe, the operator must grasp the barrel with one hand and depress the plunger with the other hand, taking care to steadily hold the syringe as the plunger is depressed. Depending on the location and direction of actuation of the thread engagement mechanism, it can be difficult to maintain the syringe in a steady position and control the thread engagement mechanism at the same time.
An additional disadvantage to such syringes is that some prior art syringes require that the barrel of the syringe be aligned in a certain orientation before the thread engagement mechanism can be actuated. This makes the syringe more difficult to use because the user must first ensure that the syringe is properly aligned before actuating the thread engagement mechanism.
A potentially serious flaw exists in known syringe designs incorporating thread engagement mechanisms. When such mechanisms are deactivated, the action of doing so causes corresponding longitudinal movement of the plunger. Such movement is unwanted, as causing potentially dangerous increases or decreases in the pressure within the balloon being inflated by the syringe.
If the balloon were to be expanded beyond acceptable limits, the coronary artery being repaired might be expanded beyond its capacity to yield. Rupture of the coronary artery would require immediate emergency surgery to correct, and, depending on the severity of the rupture, might require immediate bypass surgery.
Many prior art syringes also suffer from the disadvantage that it is impossible to view the fluid within the syringe along its entire path into the balloon catheter. During angioplasty, it is important to prevent air bubbles from entering the balloon catheter. If an air bubble were to enter the balloon and the balloon were to burst, the resulting embolism could cause serious injury to the heart and possibly result in death.
Toward this end, prior devices have relied upon priming of the locking syringe. Priming is accomplished first by placing the output end of the barrel in an elevated position. Hopefully this permits air bubbles in the fluid contents of the barrel to migrate to the output end. This process is frequently encouraged by medical personnel through shaking the syringe or tapping it with other pieces of operating room equipment. After a reasonable amount of time, the output end of the syringe is vented, and the plunger of the device is advanced into the barrel. Any entrapped air bubbles, hopefully then having moved to the output end of the syringe, are expelled with fluid through the vented end of the barrel. If successful, the remaining fluid contents of the barrel are free of air bubbles.
Nevertheless, several problems in relation to this procedure have been observed with known locking syringes. The first and most obvious of these is that of being unable to verify in any direct way that all gas bubbles have been removed from the fluid contents of the syringe.
Secondly, in the case of locking syringes normally biased into a restricted, threaded mode of operation, it has been necessary for personnel working with the syringe to simultaneously activate whatever mechanism is provided in the locking syringe to release it from its restricted, threaded mode of operation and at the same time to manipulate a syringe barrel as described above toward the end of isolating gas bubbles at the output end. Conducting these two tasks simultaneously has presented quite a challenge and has undercut the effectiveness of medical personnel in achieving the objective desired.
Apart from angioplasty, other medical applications would also benefit from a properly designed locking syringe. For example, such a syringe could be advantageously employed in a biopsy procedure to remove tissue or cell samples from a patient for later testing and laboratory examination.
In a biopsy procedure of the type contemplated, a needle is attached to the locking syringe and inserted into the body of the patient such that the end of the needle contacts the tissue desired to be sampled. The plunger is disengaged from its restricted, threaded mode of operation and rapidly withdrawn in the barrel of the syringe, creating a negative pressure within the barrel of the syringe and in the biopsy needle. The negative pressure draws sample tissue into the needle. Utilizing a locking syringe would enable the clinician to lock the plunger in this retracted position and preserves the negative pressure during withdrawal of the needle from the body of the patient.
Nevertheless, many of the problems and disadvantages discussed above with respect to angioplasty syringes also exist in syringes used for biopsy.